Business Segments - Schedule of results of operation, depreciation and amortization, capital expenditures and total assets by reportable segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Jun. 30, 2018
Net Sales:
Consolidated net sales	$ 609.9	$ 572.2	$ 1,738.8	$ 1,539.7
Operating Income:
Consolidated operating income	73.2	45.7	173.6	129.3
Depreciation and Amortization:
Consolidated depreciation and amortization	30.8	29.2	90.9	87.2
Capital Expenditures:
Consolidated capital expenditures	49.0	25.2	130.7	80.9
Total Assets:
Consolidated total assets	3,240.2		3,240.2		$ 3,007.0
Corporate
Operating Income:
Consolidated operating income	(17.3)	(18.0)	(51.5)	(44.9)
Depreciation and Amortization:
Consolidated depreciation and amortization	1.2	1.0	3.6	2.8
Capital Expenditures:
Consolidated capital expenditures	9.4	7.6	23.6	24.2
Total Assets:
Consolidated total assets	176.6		176.6		193.2
Intersegment
Net Sales:
Consolidated net sales	(17.1)	(18.1)	(50.0)	(59.3)
Operating Income:
Consolidated operating income	0.3	0.3	1.5	(2.2)
Depreciation and Amortization:
Consolidated depreciation and amortization	(0.2)	(0.1)	(0.5)	(0.6)
Capital Expenditures:
Consolidated capital expenditures	(0.3)	(0.4)	(1.1)	(0.9)
Total Assets:
Consolidated total assets	(14.7)		(14.7)		(11.9)
Specialty Alloys Operations | Operating
Net Sales:
Consolidated net sales	498.3	482.4	1,435.4	1,285.6
Operating Income:
Consolidated operating income	73.6	58.0	195.3	158.3
Depreciation and Amortization:
Consolidated depreciation and amortization	23.8	23.3	71.3	69.9
Capital Expenditures:
Consolidated capital expenditures	24.6	12.1	66.0	40.6
Total Assets:
Consolidated total assets	2,405.3		2,405.3		2,312.1
Performance Engineered Products | Operating
Net Sales:
Consolidated net sales	128.7	107.9	353.4	313.4
Operating Income:
Consolidated operating income	16.6	5.4	28.3	18.1
Depreciation and Amortization:
Consolidated depreciation and amortization	6.0	5.0	16.5	15.1
Capital Expenditures:
Consolidated capital expenditures	15.3	$ 5.9	42.2	$ 17.0
Total Assets:
Consolidated total assets	$ 673.0		$ 673.0		$ 513.6